Ni P A, Kwan J W, Roy P K, Waldron W L
Lawrence Berkeley National Laboraotry, University of California, Berkeley, California, USA.
Rev Sci Instrum. 2011 Feb;82(2):023304. doi: 10.1063/1.3555334.
The Neutralized Drift Compression Experiment-II accelerator under construction at Lawrence Berkeley National Laboratory has been designed to employ a lithium-doped alumino-silicate (Al-Si) hot-plate surface-ionization ion source. In order to achieve the design 1 mA∕cm(2) current density, the emitter must be constantly kept at a high temperature, leading to the accelerated loss of Li material as ions or neutrals. As a result, the estimated lifetime of the source is 50 h. This lifetime can be extended if the source is kept at low temperature during standby, and pulse heated to the high temperature during the ion extraction phase only. A pulsed heating technique based on an infrared laser (CO(2) gas discharge, λ = 10.6 μm) is described in this paper. The feasibility of ion current emission stimulated by flash heating with an infrared (IR) laser was demonstrated. High repeatability of the laser-stimulated ion current was observed, creating an opportunity for modulation and gating of the ion current with a laser pulse. It was found that with the available low power (≈115 W∕cm(2)) IR laser, current densities as high as 0.8 mA∕cm(2) could be achieved with a 2.8 mm diameter source. Various approaches for scaling to a larger (10 cm diameter) source and the application of short pulse, high power lasers are discussed. The results and conclusions of this paper may apply to various species of hot-plate ion sources.
劳伦斯伯克利国家实验室正在建造的中和漂移压缩实验二号加速器，设计采用掺锂铝硅酸盐（Al-Si）热板表面电离离子源。为了达到设计的1 mA∕cm²电流密度，发射极必须持续保持在高温状态，这导致锂材料以离子或中性粒子的形式加速损失。因此，该离子源的估计寿命为50小时。如果离子源在待机期间保持低温，仅在离子提取阶段脉冲加热至高温，其寿命可以延长。本文描述了一种基于红外激光（CO₂气体放电，λ = 10.6 μm）的脉冲加热技术。证明了用红外（IR）激光闪热激发离子电流发射的可行性。观察到激光激发离子电流具有高重复性，这为用激光脉冲调制和选通离子电流创造了机会。研究发现，利用现有的低功率（≈115 W∕cm²）红外激光，直径为2.8 mm的离子源可实现高达0.8 mA∕cm²的电流密度。讨论了将其扩展到更大尺寸（直径10 cm）离子源的各种方法以及短脉冲、高功率激光的应用。本文的结果和结论可能适用于各种热板离子源。
